A fuel injection valve used for an internal combustion engine for an automobile (hereinafter will be called as “engine”) comprises an electromagnetic coil, a movable valve element, a stationary core, a movable core and a spring (return spring), wherein end faces of the movable core and the stationary core are opposed to each other with a predetermined gap when the electromagnetic coil is not energized, and the return spring applies the spring load to the movable core and the movable valve element in the direction of valve-closing. The movable core is magnetically attracted toward the stationary core side against the spring force when the electromagnetic coil is energized and the movable valve element moves toward the stationary core side with the magnetic attraction to thereby make valve-opening.
Fuel is fed into a body of the injection valve from a fuel tank via a fuel pump and a fuel-feeding pipe, and is filled under pressure in a fuel passage from the inside of the hollow-stationary core to a seat portion in a nozzle body when the valve is closed. When the electromagnetic coil is energized with a fuel injection pulse signal, the valve opens only during the pulse time and fuel is injected. When the energization of the electromagnetic coil is turned off, the movable core is returned in the valve-closing direction together with the movable valve element by the return spring force and the movable valve element is pressed to the seat to make a valve-closing state.
Enhancement of a valve-closing response is of a key factor for enhancing a control accuracy of a fuel quantity of the electromagnetic injection valve. At the time when the fuel injection valve closes just after energization to the electromagnetic coil is turned off, it is known that a fluid resistance force (force due to a squeeze effect) occurs between the opposed faces of the movable core and the stationary core and that the fluid resistance force is caused by a fluid existing between the both opposed faces thereof so as to make interference against motion where the movable core removes from the stationary core. Such fluid resistance force tends to increase as the gap between the opposed faces of the movable core and the stationary core (so called fluid gap) decreases.
Conventionally, a variety of measures has been proposed for reducing such force due to squeeze effect.
For example, patent document 1 (JP-A-2003-328891) discloses that a protuberance is provided on the opposed face of a movable core with respect to a stationary core, and only this protuberance collides against the stationary core at the time of magnetic attraction so that portions other than the protuberance (non colliding portion) keep fluid gap.
Further, in place of such protuberance, patent document 2 (JP-A-2006-22727) discloses that an uneven surface of high-lying portions and low-lying portions is provided at least one of opposed faces of a movable core (armature) and a stationary core (namely, the upstream side end face of the armature and the downstream side end face of the stationary coil) by forming alternatively hard plating portions and non-plating portions on the core end face in a circumference direction thereof so as to keep fluid gaps on the low-lying portions by the height of the high-lying portions.
Still further, patent document 3 (JP-A-2005-36696) discloses that an annular collision face (a collision face with respect to a stationary core) with a limited width is provided on an annular end face of a movable core, and the collision surface is formed at an inner side with respect to a middle portion in the width direction of the annular end face of the movable core. Further, the document proposes to form tapered surfaces toward the inner side as well as the outer side from the collision surfaces and to apply anti wear plating on the annular end face. The proposed technology is intended to reduce squeeze effect by enlarging the fluid gap between the opposed faces of the movable core and the stationary core other than the collision surfaces through formation of the tapered surfaces.